Make used tex packages consistent between ps and other backends.

... by wrapping ps-specific packages in `\@ifpackageloaded`, which makes
their use transparent to the end user (if they already loaded it
themselves, we don't do anything).  So don't mention them anymore in the
matplotlibrc docs either.

Also, graphicx doesn't need the dvips option (the graphicx docs
explicitly state "normally you should... allow it to be defaulted
automatically".

(The pgf backend is a completely different beast and has its own custom
preamble anyways.)

Author: anntzer

lib/matplotlib/backends/backend_ps.py

@@ -1112,8 +1112,13 @@ def convert_psfrags(tmpfile, psfrags, font_preamble, custom_preamble,
     with mpl.rc_context({
             "text.latex.preamble":
             mpl.rcParams["text.latex.preamble"] +
-            r"\usepackage{psfrag,color}""\n"
-            r"\usepackage[dvips]{graphicx}""\n"
+            # Only load these packages if they have not already been loaded, in
+            # order not to clash with custom packages.
+            r"\makeatletter"
+            r"\@ifpackageloaded{color}{}{\usepackage{color}}"
+            r"\@ifpackageloaded{graphicx}{}{\usepackage{graphicx}}"
+            r"\@ifpackageloaded{psfrag}{}{\usepackage{psfrag}}"
+            r"\makeatother"
             r"\geometry{papersize={%(width)sin,%(height)sin},margin=0in}"
             % {"width": paper_width, "height": paper_height}
     }):

lib/matplotlib/mpl-data/matplotlibrc

@@ -319,10 +319,10 @@
                         # statements.
                         # Note that it has to be put on a single line, which may
                         # become quite long.
-                        # The following packages are always loaded with usetex, so
-                        # beware of package collisions: color, geometry, graphicx,
-                        # type1cm, textcomp.
-                        # Adobe Postscript (PSSNFS) font packages may also be
+                        # The following packages are always loaded with usetex,
+                        # so beware of package collisions:
+                        #   geometry, inputenc, type1cm.
+                        # PostScript (PSNFSS) font packages may also be
                         # loaded, depending on your font settings.
 
 ## The following settings allow you to select the fonts in math mode.

lib/matplotlib/tests/test_backend_ps.py

@@ -155,6 +155,17 @@ def test_partial_usetex(caplog):
                                   for record in caplog.records)
 
 
+@needs_usetex
+def test_usetex_preamble(caplog):
+    mpl.rcParams.update({
+        "text.usetex": True,
+        # Check that these don't conflict with the packages loaded by default.
+        "text.latex.preamble": r"\usepackage{color,graphicx,textcomp}",
+    })
+    plt.figtext(.5, .5, "foo")
+    plt.savefig(io.BytesIO(), format="ps")
+
+
 @image_comparison(["useafm.eps"])
 def test_useafm():
     mpl.rcParams["ps.useafm"] = True